Cell Membrane- active transport

What are the characteristics for carrier-mediated transport? Explain them

• saturation: ´once all available carriers are occupied, the increase of concentration molecules will not increase the rate of movement

• specific: carrier will only bind to a particular molecule

• hormone regulation: carrier mediated are regulated through these.

Vesicular transport

is the movement of substances across the membrane in membranous bags - vesicles.

Active transport because energy is required to form the vesicles

Endocytosis- processes, what is transported?

´Taking liquids or solids into the cell by vesicular transport (endo = inside).

´Cell membrane folds around particle until it is completely enclosed

´There are two types: phagocytosis and pinocytosis

´Substances transported: cholesterol, iron ions, micro-organisms and cell debris

pinocytosis

type of endocytosis, “cell drinking” transport of liquids

phagocytosis

type of endocytosis.

“cell eating”, transport of solids

Exocytosis- process, what is transported?

´When contents of a vesicle inside the cell are released to the outside (exo = outside).

´Vesicle travels to cell membrane and fuses

´Contents are pushed out into extracellular fluid

´Substances: secretions (e.g. mucus, digestive fluids, hormones)

Why are cells so small?

´A small cell will have a larger surface area to volume ratio than a large cell will

´As a cell grows its ability to exchange enough materials to support its increasing volume is lowered

• the volume increases at a greater rate than its SA.

´A large cell (with a large volume) cannot support itself as it does not have enough membrane surface to absorb all the nutrients required and remove wastes